(1) Field of the Invention
The present invention relates to a process for producing a glass doped with dispersed microcrystallites, which glass is used as a material for sharp cut filter, a material for infrared-transmitting filter, a nonlinear optical material, etc. More particularly, the present invention relates to a process for producing a glass doped with dispersed microcrystallites of CdS.sub.x Se.sub.1-x or CdS.sub.x Se.sub.1-x-y Te.sub.y.
(2) Description of the Prior Art
A glass doped with dispersed microcrystallites, comprising a matrix and microcrystallites of CdS.sub.x Se.sub.1-x (0&lt;x&lt;l) dispersed in the matrix, is in use as a material for sharp cut filter having an absorption end at the longer wavelength range of visible light. A glass doped with dispersed microcrystallites, comprising a matrix and microcrystallites of CdS.sub.x Se.sub.1-x-y Te.sub.y (0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;x+y&lt;1) dispersed in the matrix is in use as a material for infrared-transmitting filter. In recent years, the glass doped with dispersed microcrystallites, comprising a matrix and microcrystallites of CdS.sub.x Se.sub.1-x dispersed in the matrix has been found to show a third-order optical nonlinearity 8 J. Opt. Soc., Am. Vol 73, No. 5, pp. 647-653 (1983)] and has drawn attention as a nonlinear optical material for optical switch, optical computer, etc.
For producing such a glass doped with dispersed microcrystallites, there has conventionally been adopted a process which comprises melting a mixture of a glass or its materials both to become a matrix and a material to become microcrystallites dispersed in the matrix, to obtain a glass melt; cooling the glass melt to room temperature to obtain a glass comprising a matrix and ions of the elements to constitute microcrystallites, dissolved in the matrix; heating the glass to a given temperature; and maintaining the glass at that temperature to heat-treat the glass to precipitate microcrystallites in the matrix.
When a glass doped with dispersed microcrystallites is produced according to the conventional process, however, the precipitation of microcrystallites begins already at the step of heating the glass obtained by cooling the glass melt to room temperature, to a given temperature in order to precipitate microcrystallites. The microcrystallites precipitated at this step tend to cause secondary growth, i.e. a phenomenon that the elements constituting those portions of the precipitated microcrystallites having relatively small diameters are ionized and diffused into the matrix, and deposit on the microcrystallites of relatively large diameters to grow them. Such secondary growth gives rise to structural defect in precipitated microcrystallites; contamination of microcrystallites with impurities (e.g. matrix component); and structural fluctuation, whereby the precipitated microcrystallites become nonuniform.
Therefore, when a thin sharp cut filter or a thin infrared-transmitting filter is obtained from the glass doped with dispersed microcrystallites produced according to the conventional process, the spectral transmittance curve of the filter tends to be not sharp in the rise of spectral transmittance and be large in transitional interval. Accordingly, it has been difficult to obtain from said glass a sharp cut filter or an infrared-transmitting filter, both having good spectral properties.